Control of laser beam spatial and divergence distributions (“beam characteristics”) is important in many applications. In many conventional optical processing systems, a laser beam is directed to a workpiece via an optical fiber and optics that receive an optical beam from the optical fiber. While optics that receive optical beams from the optical fiber can produce selected beam characteristics, such beam characteristics tend to be difficult to vary without introducing significant complexity, cost, size, weight, optical loss, or other undesirable features into the optical system. Typically, beam characteristics at the output of the beam delivery fiber are fixed, and the optics downstream of the delivery fiber (e.g., the process head) transform the beam into one with another fixed set of characteristics (e.g., by imaging the output of the delivery fiber). As processing or other application requirements change (or in applications requiring multiple beam profiles), adapting an available laser to meet the changed requirements can be challenging for the same reasons.
Other practical issues make on-site beam modification difficult. Many high power laser systems include safety interlocks and power monitoring systems to provide operator safety and to control signals that can aid in detection of laser output anomalies that permit laser repair or adjustment prior to optical damage. Such interlocks and monitoring systems are built-in, and many desirable reconfigurations either render these safety measures ineffective, or require complex, delicate adjustments to reset.
While fiber splicing is straightforward in communication applications, introducing splices into high power laser systems can be challenging. Splices used to couple high power lasers to other fibers often must be potted, strain relieved, coated or otherwise mechanically protected, and often a splice region must be optically and thermally monitored to detect unacceptable operating conditions. Thus, splicing fibers in such applications tends to be impractical, especially for end users who generally do not have access to the processes and assembly tools used by laser manufacturers. Accordingly, improved approaches to providing variable and controllable beam profiles are needed, especially approaches adapted to reconfiguration of installed high power lasers.